ethernet: ucc_geth: remove unnecessary memset_io() calls

These buffers have all just been handed out from qe_muram_alloc(), aka
cpm_muram_alloc(), and the helper cpm_muram_alloc_common() already
does

        memset_io(cpm_muram_addr(start), 0, size);

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>